This invention relates to a method for the treatment of a water source containing water soluble polymers, especially boiler blowdown water, so as to allow the polymer containing water to be satisfactorily recycled into a recirculating cooling water system.
The use of water soluble polymeric treatment chemicals as additives to prevent scale and provide corrosion control in aqueous systems, and to disperse solids, especially in boiler water systems has gained rapid success. One of the typical components of this type of treatment is a water soluble polymer, typically a polymer or copolymer of acrylic acid or methacrylic acid, which is used to sequester hardness or scale forming cations contained in the water in the system. The additives, by effectively sequestering hardness contained in the system, prevent the deposition of hardness containing scale from the water onto the heat transfer surfaces of the aqueous system, generally a boiler water system. One of the drawbacks of such a system, is that the polymer must be present in the system in excess of the total amount of hardness present in the water. This is specifically taught in U.S. Pat. No. 4,457,847 where it is taught to treat boiler water with from 1-30 parts of polymer for each part of hardness present.
While this type of treatment maintains soluble alkaline earth metal ions in solution in boiler waters containing relatively low levels of hardness, during the usage of these boiler waters, impurities are concentrated, and as a result, most boilers discharge a portion of the concentrated impurities, along with boiler water, as boiler water blowdown. The amount of water contained in boiler water blowdown can be substantial in large boilers, and while unsuitable for further use as boiler feed water without further treatment, this water is often of a higher quality than normal, untreated feedwater. If the boiler generating the blowdown was treated with a water soluble vinyl addition polymer scale inhibitor, the addition of this untreated blowdown to a recirculating cooling water system containing water having greater than about 100ppm of hardness (calculated as CaCO3 and including scale forming cations such as calcium and/or magnesium) can result in massive quantities of undesirable polymer scale formation on the heat transfer surfaces of the recirculating water system.
The scale forming material, which is believed to be calcium or magnesium acrylate salts, fouls the heat exchange surfaces of recirculating water systems leading to the necessity to shut the system down in order to clean heat transfer surfaces and restore efficiency.
The problems associated with the use of polymer containing boiler water blowdown has prevented the widespread recycling of boiler water blowdown into recirculating cooling water systems, and as a result, large quantities of water, which while otherwise recyclable have had to have been discharged into plant waste treatment systems. This invention is directed to a method for the treatment of water, and particularly boiler water blowdown containing water soluble polymeric scale inhibitors and the like. Treatment of such waters using the method of this invention, allows the efficient and economical recycle and reuse of polymer containing waters into recirculating cooling water systems. The invention accordingly can result in substantial make-up water savings for operators of recirculating cooling water systems, while at the same time lessen the load on industrial waste water treatment facilities. By the use of the method of the present invention, the formation of polymer scale caused by the formation of alkaline earth acrylate salts on the interior surfaces of recirculating cooling water systems can be virtually eliminated.